One-step synthesis of N-doped carbon dots as sensitive "on-off-on" fluorescent sensor for tetracycline and Al3+detection

Novel bifunctional nitrogen-doped carbon dots (N-CDs) were prepared through solid-phase thermal treatment of melamine and citric acid monohydrate (CA) as precursors. The N-CDs displayed uniform size distribution, excellent photostability and bright fluorescence emission with the fluorescence quantum yield of 24 %. The N -CD-based fluorescence "on-off-on" sensing platform exhibited rapid, selective and sensitive detection of TCs (tetracycline hydrochloride and doxycycline) and Al3+. The fluorescence at 472 nm can be quenched by TCs through the internal filtration effect (IFE) and can also be recovered with the addition of Al3+ by the stronger affinity between Al3+ and TCs than that of CDs. The fluorescent sensor exhibits excellent selectivity and high sensitivity toward TCs and Al3+ detection with low detection limits for tetracycline hydrochloride: 91.8 nM, doxycycline: 78 nM and Al3+: 163.5 nM. Moreover, the proposed sensing platform is utilized for detecting TCs and Al3+ in tap water and milk samples. In addition, the N-CD probe can be used for cell imaging based on its low toxicity and good biocompatibility, implying the potential applications in the fields of biomarkers and bio-analysis in vivo imaging studies.